The present invention relates to multi-piece fasteners and more particularly to a swage type fastener having a variable clamp capability for initial fit up of workpieces and to a method for securing workpieces with an initial fit up and final clamp.
The present invention generally relates to two-piece swage type fasteners or lockbolts of the type illustrated in U.S. Pat. No. 3,915,053 to J. Ruhl, issued Oct. 28, 1975, , U.S. Pat. No. 2,531,048 to L. Huck, issued Nov. 21, 1950 and to U.S. Pat. No. 4,472,096 to J. Ruhl and R. Dixon, issued on Sep. 18, 1984. The present invention is also an improvement upon U.S. Pat. No. 4,867,625 by Richard D. Dixon for Variable Clamp Fastener and Method issued Sept. 19, 1989. In addition the present invention could utilize the groove shape and concepts of U.S. patent application Ser. No. 185,327 by Richard D. Dixon for High Strength Fastener and Method filed on Apr. 20, 1988. All of the above patents and noted patent applications can be considered as prior art relative to the present invention.
The fastener of the present invention, as with the prior art noted, includes a pin and a collar adapted to be swaged into lock grooves in the pin in response to a preselected relative axial force applied between the pin and collar.
In many commercial applications, two-piece threaded fasteners are used and are installed in two or more steps. Thus it is common to secure a structure first by attaching the associated members with the fasteners loosely engaged or torqued to be partially tightened. This facilitates adjustment and/or alignment of the structural members to a final, desired orientation even by partial loosening of the fasteners if necessary. After such adjustment and/or alignment, the fasteners are tightened to a preselected final torque. A traditional problem with torque applied threaded fasteners is that the clamp force attained is generally unpredictable due to frictional and other factors, i.e. friction between nut and engaged workpiece surfaces, friction in the engaging threads, etc. Two-piece swage type fasteners, however, are not confronted with such frictional problems and hence can provide more uniformly predictable clamp loads. Except for the construction shown in the '625 Dixon patent, however, the swage type fasteners have not been capable of providing the initial variable clamp up available with threaded fasteners and still provide a full clamp with only a second, final installation step. Prior threaded swage and/or crimp type fasteners would require extra steps or complex tooling. For example, a threaded crimp type fastener would not provide the same flexibility without complex installation tools; see for example the U.S. Pat. No. 3,421,562 to J. F. Orloff et al issued Jan. 14, 1969. While the latter fastener would permit an initial variable clamp load similar to a conventional threaded fastener, the final installation would require either two additional steps of final torquing and crimping or a complex tool capable of performing the latter steps in sequence.
In the prior art construction of the '625 Dixon patent, as in the present construction, the lock grooves of the pin are in the form of a helical male thread. The collar is provided with a mating, female thread of a preselected extent such that the initial clamp can be accommodated. The female collar thread is selected to be of a limited extent and shear strength such that the collar can be brought to its final, desired clamp position and swaged to the pin via a conventional installation tool. Thus for the final installation, a conventional pull tool can be used to apply a relative axial force between the pin and the collar. The extent of the female collar thread is selected such that, in response to the relative axial force and at a level prior to the initiation of collar deformation or swaging into the lock grooves of the pin, it will shear or deform such that the collar will be free to move axially over the pin and to respond to the installation loads in the same manner as a collar without such limited female thread form. Now the workpieces can be finally clamped together with the same effectiveness as typical swage type fasteners.
In numerous situations, the structure being built is first pre-assembled in one position or location and is then erected or moved to its ultimate position or location where the final assembly takes place. In such conditions, the fastener can be subjected to separation or handling loads of significant magnitudes. In addition, it was found in other applications that a high initial clamp load via torquing would be desirable. In such situations a significantly limited thread may not have sufficient strength to withstand such loads. Thus in such instances, these objectives could be accomplished by the use of a thread that was limited but yet comprising more or higher strength collar threads for engagement with corresponding pin threads. With a limited thread having more threads or a thread form having a higher shear strength, however, the attainment of the desired final clamp load in swage could be inhibited by the resistance of the engaged thread or threads to axial movement of the collar. Furthermore, in some applications, the workpieces could be tightly clamped in the pre-assembly step. In such cases, with the prior of the '625 Dixon patent construction, since further axial movement of the collar would be substantially precluded, shearing of the more extensive or higher strength limited thread form during swage would be inhibited whereby non-uniform final clamp loads could result between different fasteners in the same or separate structures. To overcome these problems and to permit the use of more or higher strength threads, the collar of the present invention is provided with a dished flange at its workpiece engaging end. The flange acts as a spring or resistance member such that it will resist the torque load for an initial high pre-load but can deflect or collapse upon application of the axial loads in swaging the collar for the final clamp up. Importantly, however, the dished flange will permit axial movement of the collar or of the threaded portion of the collar of at least around one half of the thread pitch such that it will not be fully collapsed until the engaged collar thread or threads have been sheared and/or deformed sufficiently to permit substantially uninhibited transfer of the relative axial force between the pin and collar to provide the desired final clamp load to the workpieces. Now sufficient threads can be employed to resist separation or handling loads in the pre-assembly and/or to permit a pre-assembly clamp load of a relatively high magnitude.
In some applications it is desirable that the fasteners have a high strength, high performance characteristic both in clamp up and in fatigue. In this latter regard then, it may be advantageous to utilize the groove shape and concepts of the invention of the '327 application and the '625 Dixon patent.
Thus, in one form of the present invention, the lock grooves in the pin are very shallow and are constructed to have roots of a simulated streamlined shape. The lock grooves are helical and define a desired thread configuration. The shallow grooves and simulated streamlined shape, however, provide a resultant fatigue life which is superior to that of a comparable threaded fastener. Since the preceding construction is shown and described in the noted patents and applications and since the present invention is not restricted to such a construction, the details thereof, while incorporated by reference, have been omitted for purposes of simplicity.
Thus it is an object of the present invention to provide a novel multi-piece swage type fastener for a fastened joint with a pin having a lock groove section with a helical thread form and with a collar adapted to be swaged into the lock groove section and having a preselected complementary threaded portion allowing a threaded connection whereby a selectively variable clamp load can be initially applied to the fastened joint prior to swage.
It is another object of the present invention to provide a novel multi-piece swage type fastener of the type noted in the preceding object in which the collar thread is adapted to be sheared or deformed at a preselected relative axial load applied by a swaging tool with that axial load being of a magnitude less than that required to initiate swaging of the collar to the pin.
It is still another object to provide a novel multi-piece, swage type fastener of the above described type in which the collar has a cooperating flange portion which is dished and deformable at a preselected axial load applied during the swage operation to permit shearing or deformation of the collar threads through relative axial movement of the pin and collar whereby attainment of the desired final clamp load upon completion of swaging is substantially uninhibited.
It is an object of the present invention to provide a multi-piece swage type fastener of the above described type having resistance means associated with the fastener which is deformable at a preselected axial load applied during the swage operation to permit shearing or deformation of the collar threads through relative axial movement of the pin and collar whereby attainment of the desired final clamp load upon completion of swaging is substantially uninhibited.
It is another general object of the present invention to provide a novel multi-piece swage type fastener.
It is still another general object of the present invention to provide a novel fastening system and method for securing workpieces utilizing a fastener and the pre-assembly of the above described type before final clamp up.